package cn.flying.cloud.base.common.utils.crypto;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * md5摘要工具类
 *
 * @author: admin
 * @date: 2022年04月02日 22:33
 * @version: 1.0
 */
public class MD5Util {
    /**
     * 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符,apache校验下载的文件的正确性用的就是默认的这个组合
     */
    protected static char[] hexDigits = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};

    private static final ThreadLocal<MessageDigest> DIGEST = new ThreadLocal<MessageDigest>() {
        @Override
        protected MessageDigest initialValue() {
            try {
                return MessageDigest.getInstance("MD5");
            } catch (NoSuchAlgorithmException e) {
                System.err.println(MD5Util.class.getName()
                        + "初始化失败，MessageDigest不支持MD5Util。");
                return null;
            }
        }
    };

    /**
     * 生成字符串的md5校验值
     *
     * @param s
     * @return
     */
    public static String md5(String s) {
        return md5(s.getBytes());
    }

    /**
     * 生成文件的md5校验值
     *
     * @param file
     * @return
     * @throws IOException
     */
    public static String md5(File file) throws IOException {
        if (!file.exists()) {
            return "";
        }
        DIGEST.get().reset();
        try (InputStream fis = Files.newInputStream(file.toPath())) {
            return md5(fis);
        } catch (Exception e) {
            return "";
        }
    }

    /**
     * 生成流的md5校验码
     *
     * @param in
     * @return
     * @throws IOException
     */
    public static String md5(InputStream in) throws IOException {
        DIGEST.get().reset();
        byte[] buffer = new byte[0x10000];
        int numRead;
        while ((numRead = in.read(buffer)) > 0) {
            DIGEST.get().update(buffer, 0, numRead);
        }
        return bufferToHex(DIGEST.get().digest());
    }

    /**
     * 生成字节的md5校验码
     *
     * @param bytes
     * @return
     */
    public static String md5(byte[] bytes) {
        DIGEST.get().reset();
        DIGEST.get().update(bytes);
        return bufferToHex(DIGEST.get().digest());
    }

    private static String bufferToHex(byte[] bytes) {
        return bufferToHex(bytes, bytes.length);
    }

    private static String bufferToHex(byte[] bytes, int n) {
        StringBuffer stringbuffer = new StringBuffer(2 * n);
        for (int l = 0; l < n; l++) {
            appendHexPair(bytes[l], stringbuffer);
        }
        return stringbuffer.toString();
    }

    private static void appendHexPair(byte bt, StringBuffer stringbuffer) {
        char c0 = hexDigits[(bt & 0xf0) >> 4];// 取字节中高 4 位的数字转换, >>>
        // 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同
        char c1 = hexDigits[bt & 0xf];// 取字节中低 4 位的数字转换
        stringbuffer.append(c0);
        stringbuffer.append(c1);
    }
}